The present invention relates to a piston type compressor for a vehicle air-conditioning system and to a method for manufacturing the piston type compressor.
Japanese Unexamined Patent Publication No. 2000-2180 discloses a swash plate type variable displacement compressor. The compressor includes a drive shaft to which the drive force is transmitted from an engine. A drive plate (swash plate) is coupled to the drive shaft such that the drive plate integrally rotates about and inclines with respect to the drive shaft. The drive plate is located in a crank chamber. Pistons are coupled to the drive plate and are accommodated in cylinder bores. The rotation of the engine is converted into the reciprocation of the pistons through the drive shaft and the drive plate. The inclination angle of the drive plate changes in accordance with the change in the difference between the pressure in the crank chamber and the pressure in the cylinder bores. The stroke of the pistons is changed in accordance with the inclination angle of the drive plate. The displacement of the compressor is changed accordingly.
A coil spring limits the axial movement of the drive shaft in a housing. The coil spring constantly presses the drive shaft in the axial direction. Limiting the movement of the drive shaft prevents the collision between the head of each piston and a valve plate when the drive shaft slides.
However, to reliably prevent the drive shaft from moving axially, the coil spring must apply a great force. This reduces the life of a thrust bearing that receives force from the coil spring and reduces the power loss of the compressor increases. The increase of the power loss of the compressor deteriorates the fuel economy of the vehicle (engine).
Therefore, a swash plate type variable displacement compressor disclosed in, for example, Japanese Examined Utility Model Publication 2-23827 is provided with a stopper (adjustment screw) that abuts against the end of a drive shaft instead of the coil spring. The stopper is threaded to a bore, in which the end of the drive shaft is accommodated, for limiting the movement of the drive shaft.
The housing and the drive shaft expand and contract by heat. The amount of deformation with respect to the same temperature changes differs between the housing and the drive shaft. This is due to the difference in the thermal expansion coefficient, which is intrinsic to each of the housing and the drive shaft. For example, when the amount of thermal contraction of the housing is greater than that of the drive shaft with respect to the same temperature changes, the space between the stopper of the housing and the drive shaft in the axial direction decreases according to the decrease of the ambient temperature. If the housing and the drive shaft continue to contract even after the space is zero, the drive shaft is pressed by the housing and the housing receives a great axial load.
The objective of the present invention is to provide a piston type compressor that prevents a drive shaft from receiving a load generated by the difference between the thermal expansion coefficient of the housing and that of a drive shaft and reduces the manufacturing cost, and to provide a method for manufacturing the piston type compressor.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, a piston type compressor is provided. The piston type compressor includes a housing, a drive shaft, a cylinder block, a valve plate, a plurality of single-headed pistons, a drive plate, a control mechanism, a contact member, a first stopper, and a second stopper. The housing defines a crank chamber. The drive shaft extends through the crank chamber and is rotatably supported by the housing. The cylinder block forms a part of the housing and defines a plurality of cylinder bores therein. The valve plate has a suction port, a suction valve, a discharge port, and a discharge valve corresponding to each cylinder bore. The valve plate is secured to the housing to close the cylinder bores. Each single-headed piston is reciprocally accommodated in one of the cylinder bores. The drive plate is located in the crank chamber and operably connected to the pistons for converting the rotation of the drive shaft to the reciprocation of the pistons. The control mechanism controls the inclination angle of the drive plate by controlling the pressure in the crank chamber to change the stroke of the pistons. The contact member is plastically deformed and press fitted to the drive shaft. The first stopper is located in the housing and limits the axial movement of the drive shaft. The first stopper limits the movement of the drive shaft in the direction away from the valve plate. The second stopper is provided in the valve plate. The second stopper limits the movement of the drive shaft toward the valve plate by the abutment with the contact member. After the contact member is attached to the drive shaft, the axial load required to change the position of the contact member is greater than the maximum axial load applied to the drive shaft due to the increase of the pressure in the crank chamber, and less than the load applied to the contact member by the second stopper in accordance with the difference in the thermal expansion coefficient of the housing and the drive shaft.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.